In recent yeas, due to the popularization of a digital camera and a cellar phone including a camera, miniaturization and a trend for high performance have been promoted. Even though, it is a small camera module, high functionalities, such as an auto-focus function, a zooming function and a correction function of camera shake have become necessary functions. In accordance with this trend, a small size actuator for moving a lens or an image sensor is required. Further, in the usage for correcting the drive of an optical pickup for recording and reproducing information onto or from DVD, the miniaturization of the actuator has been following on a course of miniaturization.
With respect to a small size actuator, which has been rapidly progressed in recent years, for example, a linear actuator including a piezoelectric element as a drive source (SIDM: Smooth Impact Drive Mechanism), a string style shape memory alloys (SMA: Shape Memory Alloys) and further a polymer actuator can be listed.
Among those items listed above, an electro static actuator using a micro processing technique, to which an integrated circuit technology called MEMS (Micro Electro Mechanical System) has bee applied, has gathered attentions. For example, Japanese Patent Application Publication Open to Public Inspection No. 2006-133730 has disclosed a method for correcting the camera shake by moving an image sensor by using a compactly shaped electro static actuator.
However, according to the method disclosed in Japanese Patent Application Publication Open to Public Inspection No. 2006-133730, the structure is arranged as following. The image sensor is placed in a sensor package; the sensor package is attached onto a flexible board; the flexible board is placed on a camera shake correction mechanism structured by the comb shaped electro static actuator. Since the image sensor, the sensor package, the flexible board and the electro static actuator are independently manufactured, the object to be driven by the electro static actuator becomes large and heavy. Accordingly, the electro static actuator securing the force power inevitably becomes large, which is not suitable for the parts to be installed into a small size camera module and an optical pickup.
Further, any countermeasure against foreign objects of the electro static actuator has not been disclosed. However, the countermeasure against foreign objects is a necessary item for the comb shaped electro static actuator and the total electro static actuator section needs to be shield. As a result, there is a problem that the size of the camera shake correction apparatus further becomes large.
In general, there are following problems to miniaturize an actuator. 1) Lowering driving load (mass of an object to be driven, friction of a mechanism, electric wiring and a convection current. 2) Simplifying assembly. 3) Lowering foreign objects. Those will be described below.
1) In general, a generated force becomes low as the size of an actuator becomes small. For example, with respect to the camera shake correction mechanism, which is a type for moving an image sensor, the lightest weight of the image sensor unit, which is an object to be moved, is about 3 g. In addition to this, when adding the friction of a mechanism, the load of a spring and the load of a flexible board for transmitting the electric signals from the image sensor to the outside, the load becomes about of 0.1N.
The volume of the actuator for driving those loads becomes about 300 mm3, which is considerably a large size. Since this size is fatal for an actuator for driving a small size camera unit and an image sensor unit of an optical pickup, it is necessary to lower the weight and load of the image sensor unit.
2) For example, in the camera shake correction mechanism, which is a type for moving an image sensor, which has been currently established, the total number of parts, which structure an actuator and the correction mechanism, is about 20, and the number of parts, which connect parts each other, is also about the same number. Taking account that applying this to a small size camera unit and an optical pickup, it is difficult to realize the contact with high accuracy in a short time period based on the extension of the conventional technique. It is necessary to make an improvement to realize it.
3) As described above, the most widely and publicly known actuator as a micro size actuator is an electro static actuator. However, for example, in the case of the comb teeth type electro static actuator, which has been described above, since the interval between a fixed comb tooth and a movable comb tooth is several μm, which is very narrow, in order to secure an operation, it is mandatory to use a sealing structure to prevent foreign objects, whose size is in a degree of several μm, from entering into the mechanism.